Turbochargers are a type of forced induction system. They compress the air flowing into an engine, thus boosting the engine's horsepower without significantly increasing weight. Turbochargers use the exhaust flow from the engine to spin a turbine, which in turn drives an air compressor. Since the turbine spins about 30 times faster than most car engines and it is hooked up to the exhaust, the temperature in the turbine is very high. Additionally, due to the resulting high velocity of flow, turbochargers are subjected to noise and vibration. Such conditions can have a detrimental Affect on the components of the turbocharger, particularly on the rotating parts such as the turbine rotor, which can lead to failure of the system.
Turbochargers are widely used on internal combustion engines and, in the past, have been particularly used with large diesel engines, especially for highway trucks and marine applications. More recently, in addition to use in connection with large diesel engines, turbochargers have become popular for use in connection with smaller, passenger car power plants. The use of a turbocharger in passenger car applications permits selection of a power plant that develops the same amount of horsepower from a smaller, lower mass engine. Using a lower mass engine has the desired effect of decreasing the overall weight of the car, increasing sporty performance, and enhancing fuel economy. Moreover, use of a turbocharger permits more complete combustion of the fuel delivered to the engine, thereby reducing the overall emissions of the engine, which contributes to the highly desirable goal of a cleaner environment. The design and function of turbochargers are described in detail in the prior art, for example, U.S. Pat. Nos. 4,705,463, 5,399,064, and 6,164,931, the disclosures of which are incorporated herein by reference.
Turbocharger units typically include a turbine operatively connected to the engine exhaust manifold, a compressor operatively connected to the engine air intake manifold, and a shaft connecting the turbine and compressor so that rotation of the turbine wheel causes rotation of the compressor impeller. The turbine is driven to rotate by the exhaust gas flowing in the exhaust manifold. The compressor impeller is driven to rotate by the turbine, and, as it rotates, it increases the air mass flow rate, airflow density and air pressure delivered to the engine cylinders.
As the use of turbochargers finds greater acceptance in passenger car applications, three design criteria have moved to the forefront. First, the market demands that all components of the power plant of either a passenger car or truck, including the turbocharger, must provide reliable operation for a much longer period than was demanded in the past. That is, while it may have been acceptable in the past to require a major engine overhaul after 80,000-100,000 miles for passenger cars, it is now necessary to design engine components for reliable operation in excess of 200,000 miles of operation. It is now necessary to design engine components in trucks for reliable operation in excess of 1,000,000 miles of operation. This means that extra care must be taken to ensure proper fabrication and cooperation of all supporting devices.
The second design criterion that has moved to the forefront is that the power plant must meet or exceed very strict requirements in the area of minimized NOx and particulate matter emissions. Third, with the mass production of turbochargers, it is highly desirable to design a turbocharger that meets the above criteria and is comprised of a minimum number of parts. Further, those parts should be easy to manufacture and easy to assemble, in order to provide a cost effective and reliable turbocharger. Due to space within the engine compartment being scarce, it is also desirable that the overall geometric package or envelope of the turbocharger be minimized.
In Japanese Patent Application No. 2000257437A2 to Hiroyuki, a compressor section for a turbocharger is shown which attempts to increase the work load of the pressure conversion by elongating the diffuser. In FIG. 1, an extended diffuser 22 is formed in a compressor housing 18 which is in communication with the compressor impeller 17, the impeller chamber 21 and the scroll 23. The diffuser 22 has an elongated, straight portion 22A extending from the inlet 25A of the diffuser. An end 22B along the outlet portion 25B of the diffuser is bent to provide the fluid communication between the scroll 23 and the diffuser 22.
The Hiroyuki system also suffers from the drawback of requiring a large envelope to account for the length of the diffuser 22. The increased envelope adds cost to the system by requiring more material to be used, such as for compressor housing 18.
U.S. Pat. No. 6,679,057 to Arnold shows a turbocharger with a compressor section having a compressor wheel and movable guide vanes. As shown in FIG. 2, the Arnold system has a turbocharger 110 with a turbine housing 112 adapted to receive exhaust gas from an internal combustion engine and distribute the exhaust gas to an exhaust gas turbine wheel or turbine 114 rotatably disposed within the turbine housing 112 and coupled to one end of a common shaft 116. The turbine housing 112 encloses a variable geometry system that comprises a plurality of pivotably moving vanes 118. A turbine unison ring 119 engages the vanes 118 to effect radially inward and outward movement thereof The turbine unison ring 119 comprises a plurality of slots 120 that correspond with tabs 122, and an elliptical slot 123 that is configured to accommodate placement of an actuator pin 124 therein for purposes of moving the unison ring. The pin 124 is attached to an actuator lever arm 126 and an actuator crank 128 which are disposed within a portion of the turbocharger center housing 130. The actuator crank 128 is rotatably disposed axially through the turbocharger center housing 130, and is configured to move the lever arm 126 back and forth about an actuator crank longitudinal axis, which movement operates to rotate the actuating pin 124 and effect rotation of the unison ring 119 within the turbine housing.
The turbocharger 110 also comprises a compressor housing 131 that is adapted to receive air from an air intake 132 and distribute the air to a compressor impeller 134 rotatably disposed within the compressor housing 131 and coupled to an opposite end of the common shaft 116. The compressor housing 131 also encloses a variable geometry member 136 interposed between the compressor impeller 134 and an air outlet. The variable geometry member 136 is positioned in a straight, radial diffuser 175 and comprises a plurality of pivoting vanes 138. The diffuser 175 is connected with volute 180, which is formed along an outer region and radially remote from the impeller 134.
A compressor unison ring 140 is rotatably disposed within the compressor housing 131 and is configured to engage and rotatably move all of the compressor vanes 138 in unison. The compressor unison ring 140 comprises a plurality of slots 142 that correspond with tabs 144 projecting from each respective compressor vane. The compressor adjustment ring 140 comprises a slot and an actuating pin 146 that is rotatably disposed within the slot. An actuating lever arm 148 is attached to the actuating pin 146 and to the actuator crank 128. The actuating pin 146 and lever arm 148 are disposed through a backing plate 150 that is interposed between the turbocharger compressor housing 131 and the center housing 130. Rotation of the actuating pin 146 causes the compressor unison ring 140 to rotate along the backing plate 150.
The Arnold system suffers from the drawback of requiring a large envelope to account for the length of the diffuser 175 and the moveable guide vanes 138 positioned therein. The increased envelope adds cost to the system by requiring more material to be used, such as for the compressor housing 131.
In FIG. 3, a portion of a contemporary compressor housing 200 is shown having a scroll 220 and a flat radial diffuser 250. Diffuser 250 lies along diffuser plane PFD, which is formed along an outer circumference of the scroll 220. To increase the diffuser length, the contemporary turbocharger requires that the geometric envelope of the turbocharger be increased. The increased envelope adds cost to the system by requiring more material to be used, such as for a compressor housing.
Thus, there is a need for a turbocharger system, and method of manufacturing such a system, that effectively and efficiently controls fluid flow from the compressor wheel. There is a further need for such a system that maximizes diffusion without increasing the size of the geometric envelope. There is yet a further need for such a system and method of manufacturing such a system that is reliable and cost-effective.